In hard disk drives, data is written to and read from magnetic recording media, herein called disks. Typically, one or more disks having a thin film of magnetic material coated thereon are rotatably mounted on a spindle. A read/write head mounted on an actuator arm is positioned in close proximity to the disk surface to write data to and read data from the disk surface.
During operation of the disk drive, the actuator arm moves the read/write head to the desired radial position on the surface of the rotating disk where the read/write head electromagnetically writes data to the disk and senses magnetic field signal changes to read data from the disk. Usually, the read/write head is integrally mounted in a carrier or support referred to as a slider. The slider generally serves to mechanically support the read/write head and any electrical connections between the read/write head and the disk drive. The slider is aerodynamically shaped, which allows it to fly over and maintain a uniform distance from the surface of the rotating disk. Typically, the read/write head includes a magnetoresistive read element to read recorded data from the disk and an inductive write element to write the data to the disk.
Various types of magnetoresistive sensor technology for read elements have been developed (AMR, GMR, TuMR, for example). For each of these, a bias current is directed through a magnetoresistive sensing layer. The magnetic field stored in the adjacent disk affects the resistance of this sensing layer. With a read bias current of a known magnitude, the voltage drop across the read sensor can be measured and the resistance calculated therefrom. In this manner, the sensor can detect the changing magnetic fields of each recorded bit on the adjacent spinning magnetic disk. Over the past five years or so, with each new generation of disk drive systems having smaller spacing between the head and disk, smaller spacing between adjacent tracks on the disk, and smaller spacing between adjacent bits on a given track on the disk, more sensitive read sensors are being employed.
Unfortunately, these more-sensitive read sensors occasionally experience glitches or current spikes of relatively high magnitude in the bias current. These glitches can occur for a variety of reasons, including electrostatic discharge (ESD) shock, sparks from contact between the head and the disk, unintentional injection of current into the head, cross-talk between the read sensor and write head, and other factors. Such glitches may result in degradation, damage, or failure of the read head.
These glitches can occur while reading data or while not reading data, during transitions between various operational modes, or in various different operational conditions. Glitches may occur in heads produced by one head manufacturer using a given fabrication process while not occurring in heads of identical design using another fabrication process.
Disk drive manufacturers may typically perform a failure analysis of the disk drive system to determine why certain manufactured heads failed. It is very difficult to replicate or detect the glitch when analyzing the disk drive system in the laboratory, for a variety of reasons.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.